On Monday 24 January 2005 03:13 am, Vaibhav Sharma, Noida wrote: > According to the design of UML, it has its own VM system. If I have to > check the scalability limits of the "parent kernel" for memory management, > will UML be useful..?
Jeff Dike already answered this. (He's the UML maintainer.) UML _does_ remap a different chunk out of the physical memory backing file when it schedules a different process. UML uses mmap to get its memory, so as long as the parent kernel has Large File Support (which lets a 32 bit machine use 64 bit file offsets, this is pretty widely deployed because people need a single file to be larger than INT_MAX, which is 2 gigabytes since file offsets are signed for some reason), and the UML instance is configured to use highmem (which is what unmaps and remaps the memory on a schedule) and at least 3 level page tables (so it doesn't run out of PTEs), UML shouldn't be limited to 32 bits of (simulated) physical memory. Not that I've tried this. :) An individual process running under a 32-bit UML would still only be able to access 4 gigabytes or less. (It has a 32 bit virtual address space, after all...) And since I'm unaware of any version of UML using the 4 gig/4 gig patch, I suspect UML might fill up its kernel memory area with page table entries eventually... (Was Dave Jones's shared page table patch ever integrated? Are linux page tables swappable?) > When I debug the UML kernel when a process requests a large amount of > memory, I will only get the flow used by UML for its VM. Is the code/design > of UML very different from the parent kernel..? UML uses mmap on a file to simulate an MMU. It shouldn't care what kind of physical memory the parent kernel has. But Jeff's the expert here. However running 'find arch/um -name "*.c" | xargs grep mmap' in your linux source directory should get you started. > (I may be totally wrong in this mail, please do correct me...) I'm not the world's greatest source of info here either, I've only been playing with UML for a little while... Rob ------------------------------------------------------- This SF.Net email is sponsored by: IntelliVIEW -- Interactive Reporting Tool for open source databases. Create drag-&-drop reports. Save time by over 75%! Publish reports on the web. Export to DOC, XLS, RTF, etc. Download a FREE copy at http://www.intelliview.com/go/osdn_nl _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
